Hasil untuk "Geomagnetism"

近角 聡信, S. Charap

Reginaldo Lemos, Manoela Bettarel Bállico, Marcelo Accioly Teixeira De Oliveira et al.

The Rio do Rasto and Botucatu Formations represent the main aquifer reservoirs in the state of Santa Catarina Brazil. The vertical facies succession of these formations comprises reservoirs formed by a complex fluvial-eolian interaction. The analysis of the depositional architecture, the use of geophysical data and of high-resolution virtual outcrop models from these reservoirs improved the understanding and of high-resolution heterogeneities at different scales and allowed the development of lithological and aquifer models that demonstrate this interaction. At megascopic scale, the reservoirs are composed of fine-grained sediments interbedded with with sandy bodies deposited in a fluvio-eolian context of the Rio do Rasto Formation, and large-scale eolian dunes deposited in a dry eolian system of the Botucatu Formation. At macroscopic scale, the fluvial-interpreted reservoir presented more vertical and lateral heterogeneities relative to the eolian reservoir. Unconformity surfaces and clay layers act as its main flow barriers. At mesoscopic heterogeneity reflects lithofacies and sedimentary structures within eolian and fluvial facies associations. In this scale the major parameters that impact the flow migration are textural and structural differences associated with eolian and fluvial depositional processes.

Nathalia Martinho Cruz, Thais Pontes Bispo, Adler Nascimento et al.

The Aptian carbonate reservoirs within the pre-salt section of the Santos Basin, such as the principal reservoirs of the Tupi Field, exhibit considerable heterogeneity in reservoir quality. This variability is influenced by several factors, including the widespread presence of magnesium clay minerals and diagenetic processes, which hampers hydrocarbon production. Given the lack of comprehensive reservoir-scale historical references, we revisit the reservoir zoning, inherent individualizations, facies distributions, seismostratigraphic, and tectonic features of the Barra Velha Formation within the Tupi Field. We spatially map key elements, decipher facies association profiles, and pinpoint porosity classes tied to facies and depositional or diagenetic characteristics from a multi-scale dataset comprising rock samples, well logs, and seismic data. A pragmatic seismostratigraphic zoning approach was employed to define intervals BVE100, BVE200, and BVE300 and their subzones. Reservoir quality was then linked with lake retraction periods, identified by an increase in well-developed shrubs displaying higher porosities and permeabilities, properties further amplified by dissolution phenomena. We also discuss the influence of structural positioning on facies distribution, associating higher carbonates with clay minerals proportions to structural lows, and reworked carbonates reservoirs to the structural highs and edges. We argue that only the BVE100 displays sag-type features, suggesting a mixed tectonic setting for BVE200. Furthermore, we characterized Feature X, a unique BVE100 high acoustic impedance signature associated with wells sampling elevated proportions of low-energy facies within structural flanks and lows. These insights carry significant implications for exploration and exploitation strategies in the studied area and can be applied to other pre-salt regions of any basin.

Guilherme Bravo Braus, Sergio Antonio Gimenez Junior, Breno Padovezi Rocha et al.

This paper presents the updated version of a system that uses a probe and software to carry out down-hole seismic testing in conjunction with piezocone to determine shear wave (Vs) and compressional wave (VP) velocities for geotechnical site characterization. The system was used in down-hole tests carried out at experimental research sites located in the interior of the state of São Paulo, Brazil, where reference Vs and VP values determined by cross-hole and down-hole tests are available. The updated seismic probe has six geophones: three for S wave recordings spaced 0.5 m apart and three for P wave recordings, also spaced 0.5 m apart. The updated software integrates data acquisition, allows the visualization of S and P wave traces and calculates Vs using the true interval method. The VP profiles could only be determined by the pseudo-time interval using commercial software. The developed system is considered efficient for determining Vs profiles in the way it was used. Further studies are needed to better understand the propagation of P waves, as well as to improve the system and the method for determining VP profiles.

Love Jeffrey J., Rigler E. Joshua, Hayakawa Hisashi et al.

A study is made of the intensity of the Carrington magnetic storm of September 1859 as inferred from visual measurements of horizontal-component geomagnetic disturbance made at the Colaba observatory in India. Using data from modern observatories, a lognormal statistical model of storm intensity is developed, to characterize the maximum-negative value of the storm-time disturbance index (maximum –Dst) versus geomagnetic disturbance recorded at low-latitude observatories during magnetic storms. With this model and a recently published presentation of the Colaba data, the most likely maximum –Dst of the Carrington storm and its credibility interval are estimated. A related model is used to examine individual Colaba disturbance values reported for the Carrington storm. Results indicate that only about one in a million storms with maximum –Dst like the Carrington storm would result in local disturbance greater than that reported from Colaba. This indicates that either the Colaba data were affected by magnetospheric-ionospheric current systems in addition to the ring current, or there might be something wrong with the Colaba data. If the most extreme Colaba disturbance value is included in the analysis, then, of all hypothetical storms generating the hourly average disturbance recorded at Colaba during the Carrington storm, the median maximum –Dst = 964 nT, with a 68% credibility interval of [855,1087] nT. If the most extreme Colaba disturbance value is excluded from the analysis, then the median maximum –Dst = 866 nT, with a 68% credibility interval of [768,977] nT. The widths of these intervals indicate that estimates of the occurrence frequency of Carrington-class storms are very uncertain, as are related estimates of risk for modern technological systems.

Chinmaya Nayak, Jayashree Bulusu, Geeta Vichare et al.

Abstract The current study explores the relationship between solar variability and tropical cyclone (TC) activity using sunspot number (SSN) and TC best‐track data as respective proxies. We have considered six regions of the globe, for example, EP: Eastern Pacific, NA: North Atlantic, NI: North Indian, SI: South Indian, SP: South Pacific, and WP: Western Pacific. The results show strong anti‐correlation between yearly TC activity and yearly SSN while considering their 11‐year moving averages. This behavior is consistent for TC counts as well as accumulated cyclone energy. However, this is true only for the North Atlantic region. Overall, when we consider all regions together, more TCs (in terms of counts) are observed during lower solar activity periods (SSN < 50) as compared to higher solar activity conditions (SSN > 100). However, the yearly rates remain more or less similar. On the other hand, extreme TC events with a maximum wind speed of 137 knots and higher (category 5) are most likely to occur during the declining phase of a solar cycle and least likely to occur during the ascending phase or the maximum phase. Although solar activity levels are similar during the declining and ascending phases, the yearly occurrence rate is nearly double in the declining phase (1.123) as compared to that in the ascending phase (0.625).

Ciaran D. Beggan, Eliot Eaton, Eleanor Maume et al.

Abstract Continuous geomagnetic records of the strength and direction of the Earth's field at the surface extend back to the 1840s. Over the past two centuries, eight observatories have existed in the United Kingdom, which measured the daily field variations using light‐sensitive photographic paper to produce analogue magnetograms. Around 350,000 magnetograms have been digitally photographed at high resolution. However, converting the traces to digital values is difficult and time consuming as the magnetograms can have over‐lapping lines, low quality recordings and obscure metadata for conversion to SI units. We discuss our approach to digitizing the traces from large geomagnetic storms and highlight some of the issues to be aware of when capturing magnetic information from analogue measurements. These include cross‐checking the final digitized values with the recorded hourly mean values from observatory year books and comparing several observatory records for the same storm to catch errors such as sign inversions or incorrect ‘wrap‐around’ of data on the paper records.

Witali Krochin, Gunter Stober, Axel Murk

This article addresses the further development of the ground-based temperature radiometer TEMPERA, which measures atmospheric microwave radiation in one linear polarization in order to retrieve temperature profiles up to an altitude of 50 km (St&#x00E4;hli <italic>et al.</italic>, 2013). The latest innovation is a new polarimetric receiver, which allows observing the atmosphere simultaneously in left- and right-circular polarization. In combination with an adapted inversion method, the fully polarimetric analysis can improve the accuracy and extends the vertical upper limit of retrieved temperature profiles. Comparisons between single polarization and fully polarimetric retrievals with simulated atmospheric spectra are presented, and the influence of the Earth&#x2019;s magnetic field is analyzed. In addition, we propose a simple calibration method for fully polarimetric radiometers and present first atmospheric spectra measured with the new TEMPERA-C instrument.

Masafumi Shoji, Yoshizumi Miyoshi, Lynn M. Kistler et al.

Abstract A study using Arase data gives the first observational evidence that the frequency drift of electromagnetic ion cyclotron (EMIC) waves is caused by cyclotron trapping. EMIC emissions play an important role in planetary magnetospheres, causing scattering loss of radiation belt relativistic electrons and energetic protons. EMIC waves frequently show nonlinear signatures that include frequency drift and amplitude enhancements. While nonlinear growth theory has suggested that the frequency change is caused by nonlinear resonant currents owing to cyclotron trapping of the particles, observational evidence for this has been elusive. We survey the wave data observed by Arase from March, 2017 to September 2019, and find the best falling tone emission event, one detected on 11th November, 2017, for the wave particle interaction analysis. Here, we show for the first time direct evidence of the formation of a proton hill in phase space indicating cyclotron trapping. The associated resonance currents and the wave growth of a falling tone EMIC wave are observed coincident with the hill, as theoretically predicted.

Kuznetsov Vladimir

Principally new quantum model of the magnetic field of the Hot Earth [1] is proposed here. The model proceeds from the generation scheme of the Earth magnetic field (EMF) reported at the conference in 2019 [2], where crucial role of quantum entanglement (QE) of the inner G-core matter for EMF generation under the Hall effect was first evidenced. With regard to my impact into geodynamics of the Hot Earth [3] and quantum geophysics [4] the improved version of [2] is presented here. The justification for the model of EMF generation given in the encyclopedia of Geomagnetism [5] due to the daily rotation of the DEL (double electric layer), exciting a weak field and its amplification by the Hall current is first used here.

Valach Fridrich, Hejda Pavel, Revallo Miloš et al.

Some recent studies point out that currents related to the auroral oval, electrojets and field aligned currents (FACs), are serious candidates for the mechanism of the intense mid-latitude magnetic storms. It is interesting to re-analyse historical data under the light of this modern knowledge. In this aim, we analysed two intense magnetic storms that were recorded by observatories Clementinum (Prague) and Greenwich on 17 November 1848 and 4 February 1872, respectively. The latter has been marked as an extraordinary event by several authors, in particular in connection with auroras. The former, however, has been little known in the space weather community. Both these events possessed swift and extensive variations of the horizontal (H) component (>400 nT and >500 nT, respectively) and were accompanied by auroras sighted at very low magnetic latitudes. This implies that the auroral oval on the north hemisphere was vastly extended southward. The variations of the magnetic declination also indicate that during these events the auroral oval was situated at magnetic latitudes lower than those of the observatories. The storms studied in this paper occurred at different magnetic local times (MLTs), ~23 MLT and ~19 MLT. Therefore, they might represent mid-latitude events related to different parts of the auroral oval. In this paper, the H-variation recorded at Clementinum in 1848 is interpreted to be a substorm due to the ionospheric substorm electrojet. The Greenwich event registered in 1872 then seems to be a combination of the ring-current storm with a positive variation of the H-component caused by the eastward electrojet. Both the events of 1848 and 1872 appear to exemplify phenomena that are common in high magnetic latitudes but which may occasionally happen also at mid-latitudes.

Dhanya Thomas, Mala S. Bagiya, Poikayil Sukumaran Sunil et al.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Ayako Matsuoka, Mariko Teramoto, Reiko Nomura et al.

Abstract The fluxgate magnetometer for the Arase (ERG) spacecraft mission was built to investigate particle acceleration processes in the inner magnetosphere. Precise measurements of the field intensity and direction are essential in studying the motion of particles, the properties of waves interacting with the particles, and magnetic field variations induced by electric currents. By observing temporal field variations, we will more deeply understand magnetohydrodynamic and electromagnetic ion-cyclotron waves in the ultra-low-frequency range, which can cause production and loss of relativistic electrons and ring-current particles. The hardware and software designs of the Magnetic Field Experiment (MGF) were optimized to meet the requirements for studying these phenomena. The MGF makes measurements at a sampling rate of 256 vectors/s, and the data are averaged onboard to fit the telemetry budget. The magnetometer switches the dynamic range between ± 8000 and ± 60,000 nT, depending on the local magnetic field intensity. The experiment is calibrated by preflight tests and through analysis of in-orbit data. MGF data are edited into files with a common data file format, archived on a data server, and made available to the science community. Magnetic field observation by the MGF will significantly improve our knowledge of the growth and decay of radiation belts and ring currents, as well as the dynamics of geospace storms.

S. K. Bhardwaj, P. B. V. Subba Rao

Abstract In the present study, the technique of principal component analysis (PCA) is applied to analyze the hourly mean values of geomagnetic field components D, H, and Z along an Indo-Russian chain of stations during the International Equatorial Electrojet Year (IEEY) from January 1992 to June 1993. This technique (PCA) is found to be suitable for separating the normal electrojet (NEJ) and counter-electrojet (CEJ) variations, and the first two principal components (PCs) are able to describe the characteristics of NEJ- and CEJ-related field variations. It is found that the first principal component (PC-1) for H, D, and Z varies as a function of time with latitude and depicts the well-known Sq variations, whereas PC-2(H) does not show any variations at all latitudes during NEJ days. On CEJ days, PC-2(H) shows a large negative excursion at equatorial stations (KAN to BAN). The NEJ- and CEJ-related current systems are determined by combining the hourly inequalities in D and H. PC-1 brings out a well-defined anticlockwise loop for NEJ days, with its focus near the dip latitude (~35°N), and a clockwise loop for CEJ days with a well-defined focus near the dip latitude (~20°N) around noon local time. The CEJ-related current system is marked by intense westward current flow in the equatorial belt and is shown to close its path by forming a clockwise loop extending from the dip equator to midlatitudes. Comparison with a numerically simulated current system, caused by various tidal modes, emphasizes the significance of antisymmetric semidiurnal tidal modes in the generation of CEJ events. Graphical abstract .

Nagarjuna Danda, C. K. Rao, Amit Kumar

Abstract Broadband and long-period magnetotelluric data were acquired over the northern part of the Cambay rift zone along an east–west profile ~ 200 km in length. The decomposed TE- and TM-mode data were inverted using a 2-D nonlinear conjugate gradient algorithm to obtain the lithospheric structure of the region. A highly conductive (~ 1000 S) layer was identified within the Cambay rift zone and interpreted as thick Quaternary and Tertiary sediments. The crustal conductors found in the profile were due to fluid emplacement in the western part, and the presence of fluids and/or interconnected sulfides caused by metamorphic phases in the eastern part. The demarcation of the Cambay rift zone is clearly delineated with a steeply dipping fault on the western margin, whereas the eastern margin of the rift zone gently dips along the NE–SW axis, representing a half-graben structure. A highly resistive body identified outside the rift zone is interpreted as an igneous granitic intrusive complex. Moderately conductive (30–100 Ω-m) zones indicate underplating and the presence of partial melt due to plume–lithosphere interactions.

Guan Le, James A. Slavin, and Robert F. Pfaff

In studying the _ geomagnetism it has always been a challenge to separate the external currents originating from the ionosphere and magnetosphere. While the internal magnetic field changes very slowly in time scales of years and more, the ionospheric and magnetospheric current systems driven by the solar wind-magnetosphere interaction are very dynamic. They are intimately controlled by the ionospheric electrodynamics and ionosphere-magnetosphere coupling. Single spacecraft observations are not able to separate their spatial and temporal variations, and thus to accurately describe their configurations. To characterize and understand the external currents, satellite observations require both good spatial and temporal resolutions. This paper reviews our observations of the external currents from two recent Low Earth Orbit (LEO) satellite missions: Space Technology 5 (ST-5), _ first three-satellite constellation mission in LEO polar orbit and Communications/Navigation Outage Forecasting System (C/NOFS), an equatorial satellite developed by the US Air Force Research Laboratory. We present recommendations for future geomagnetism missions based on these observations.

V. Yadav, B. Kakad, C. K. Nayak et al.

A thin and highly dense sporadic E layer, which can occasionally block the upper ionospheric layers, is called blanketing sporadic E (E_sb). We present the statistical seasonal local time occurrence pattern of E_sb at equatorial station Tirunelveli (8.7° N, 77.8° E, dip latitude 0.7° N) during the extended minimum of solar cycle 24 (2007–2009). In spite of nearly the same average solar activity during both 2007 and 2009, considerable differences are noticed in the seasonal occurrence of E_sb during this period. The percentage of E_sb occurrence is found to be the highest during the summer solstice (&geq; 50%) for both 2007 and 2009, which is in general accordance with the earlier studies. The occurrences of E_sb during the vernal equinox (~ 33%) and January–February (~ 28%) are substantial in 2009 as compared to those during the same seasons in 2007. We find that, during winter (January–February), ~ 75% of E_sb occurred during or just after the period of sudden stratospheric warming (SSW). We suggest that enhanced E_sb occurrence during winter (January–February) and the vernal equinox of 2009 could be associated with SSW-driven changes in the E region ambient conditions. Furthermore, the close association of E_sb with counter equatorial electrojet (CEEJ) suggested by earlier studies is re-examined carefully using the scenario of E_sb occurrence on non-CEEJ days. Such an exercise is crucial as we are unaware whether the physical mechanisms driving E_sb and CEEJ are linked or not. We find that, of all the seasons, the association of E_sb and CEEJ is strongest during winter (November–December).

C. Voorhies

J. L. Zerbo, J. L. Zerbo, C. Amory Mazaudier et al.

We examined solar activity with a large series of geomagnetic data from 1868 to 2009. We have revisited the geomagnetic activity classification scheme of Legrand and Simon (1989) and improve their scheme by lowering the minimum Aa index value for shock and recurrent activity from 40 to 20 nT. This improved scheme allows us to clearly classify about 80% of the geomagnetic activity in this time period instead of only 60% for the previous Legrand and Simon classification.

C. K. Nayak, D. Tiwari, D. Tiwari et al.

In this paper we present a case study of the annular solar eclipse effects on the ionization of E and F regions of equatorial ionosphere over Tirunelveli [77.8° E, 8.7° N, dip 0.4° N] by means of digital ionosonde on 15 January 2010. The maximum obscuration of the eclipse at this station was 84% and it occurred in the afternoon. The E and F1 layers of the ionosphere showed very clear decrease in their electron concentrations, whereas the F2 layer did not show appreciable changes. A reduction of 30% was observed in the <I>fo</I>F1 during the maximum phase of the eclipse. During the beginning phase of the eclipse, an enhancement of 0.97 MHz was observed in the <I>fo</I>F2 as compared to that of the control days. But the <I>fo</I>F2 decreased gradually as the eclipse progressed and a decrease of 0.59 MHz was observed towards the end phase of the eclipse. Observed variations in the <I>h</I>'F2 and <I>hm</I>F2 showed lower values than the control days, although <I>hm</I>F2 was found to increase a bit during the eclipse. Observed variability in the E, F1 and F2 layer ionospheric parameters on the eclipse day and their departure from the control days are discussed as the combined effect of annular eclipse and presence of counter equatorial electrojet (CEEJ).